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Proof of the Hodge Conjecture - Final Write-Up.
by Philip White.
October 22, 2021
An “easily understood summary” will follow at the end.
I. PROBLEM STATEMENT DEFINITIONS
- A claim that I need to verify: One subset of the set of all Hodge Classes is the set of all valid morphisms (i.e., continuous functions) from, given all finitely bounded manifolds M in P^2, M to the complex plane. I.e., we define the subset P^2_HC of HC as follows: (P^2_HC (subset of) HC) = { X | M is a manifold in P^2 and X is a morphism from M to C } .
- Fix an arbitrary algebraic variety V (an algebraic variety is a set of solutions to a system of polynomial equations, in this case in P^2). A class is a set with a restriction on membership defined by a wf. Given a fixed arbitrary algebraic variety V, an algebraic cycle is a rational linear combination of classes of algebraic subvarieties of V. (The points are treated as vectors, and the "sum" of the classes represents all possible sums of vectors from the individual classes.)
- An m-manifold is a topological space such that for each point in the main set X, the neighborhood of that point in the space is homeomorphic to m-dimensional Euclidean space.
- Given a topological space X and a point p in X, a neighborhood of p is a subset V or X such that an open set U is such that p is an element of U and U is a subset of V.
II. SWISS CHEESE MANIFOLDS AND KEY CORRESPONDENCE FUNCTION.
Consider P^2. Think of an infinite piece of Swiss cheese (or an infinite standardized test scantron sheet with answer bubbles to bubble in), where every integer point pair (e.g., (5,3) , (7,7) , (8,6) , etc.) is surrounded by a small empty circular area with no points. The Swiss cheese piece is infinite; it doesn't matter that it is a subset of P^2 and not of R^2. We will fill in the full empty holes associated with each point that is an ordered pair of integers in the Swiss cheese piece based on certain criteria. Note that every point in the manifold is indeed in neighborhoods that are homeomorphic to 2-D Euclidean space, as desired (the Swiss cheese holes are perfect circles of uniform size, with radius 0.4).
Now, consider a fixed arbitrary subset S of Z x Z. We modify the Swiss cheese manifold in P^2, filling in each empty circular hole associated with each ordered pair that is an element of S in the Swiss cheese manifold, with all previously omitted points in the empty circular holes included; this could be thought of as “bubbling in some answers into the infinite scantron”. Let F1 : PowerSet(Z x Z) --> PowerSet(P^2) be this correspondence function that maps each subset of Z x Z to its associated Swiss cheese manifold.
Define an arbitrary morphism M : P^2_HC --> C, and let MS be the set containing all such valid functions M. Let the key correspondence function F2 : PowerSet (Z x Z) --> MS map every element S of PowerSet(Z x Z) to the least element of a well-ordering of the subset MS2 of MS such that all elements of MS2 are functions that map elements of F1(S) to the complex plane, which must exist due to the axiom of choice. (Note, we could use any morphism that maps a particular S.C. manifold to the complex plane. Also note, at least one morphism always exists in each case.)
For clarity: Basically, F2 maps every possible way to fill in the Swiss cheese holes to a particular associated morphism, such that this morphism itself maps the filled-in Swiss cheese manifold based on this filling-in scheme to the complex plane.
III. VECTOR AXIOMS, AND VECTOR INFERENCE RULE DEFINITIONS.
Now we define “vector axioms” and “vector inference rules.”
Each "vector axiom" is a “vector wf” that serves as an axiom of a formal theory and that makes a claim about the presence of a vector that lies in a rectangular closed interval in P^2, e.g, "v1 = <x,y>, where x is in [0 - 0.2, 0 + 0.2] and y is in [2 - 0.2, 2 + 0.2]". The lower coordinate boundaries (a=0 and b=2, here) must be integer-valued. The vector will be asserted to be a single fixed vector that begins at the origin, (0,0), and has a tail in the rectangular interval. The "vector formal theory inference rules” will be Turing machines based on rational-valued vector artihmetic—there are infinitely many such rules, of three types: 1) simple vector addition, 2) multiplication of a vector by a scalar integer, and 3) division of a vector by a scalar integer—that reject or accept all inputs, and never fail to halt; the output of these inference rules, given one or two valid axioms/theorems, is always another vector wf, which is a valid theorem. Note that class restrictions can be coded into these TMs; i.e., these three types of inference rules can be modified to exclude certain vector wfs from being theorems. The key "vector wfs” will always be in a sense of the form "v_k = <x,y> where the x-coordinate of v_k is in [a-0.2,a+0.2] and the y-coordinate of v_k is in [b-0.2,b+0.2] ". We will define the predicate symbol R1(a,b) to represent this, and simply define a large set of propositions of the form "R1(a,b)”, with a and b set to be fixed constant elements of the domain set of integers, as axioms. All axioms in a "vector formal theory" will be of this form, and each axiom can be used in proofs repeatedly. Given a fixed arbitrary class of algebraic cycles A, we can construct an associated "vector formal theory" such that every point in A that is present in certain areas of P^2 can be represented as a vector that is constructible based on linear combinations of and class restriction rules on, vectors. The key fact about vector formal theories that we need to consider is that for a set of points T in a space such that all elements of T are not elements of the classes of algebraic cycles, any associated vector wf W is not a theorem if the set of all points described by W is a subset of T. In other words, if an entire "window of points" is not in the linear combination, then the proposition associated with that window of points cannot be a theorem. Also, if any point in the "window of points" is in the linear combination, then the associated proposition is a theorem.
(Note: Each Swiss cheese manifold hole has radius 0.4, and the distance from the hole center to the bottom left corner of any vector-axiom-associated square region is sqrt(0.08), which is less than 0.4 .)
Importantly, given a formal vector theory V1, we treat all theorems of this formal theory as axioms of a second theory V2, with specific always-halting Turing-machine-based inference rules that are fixed and unchanging regardless of the choice of V1. This formal theory V2 represents the linear combinations of V1-based classes of algebraic cycles. The full set of theorems of V2 represents the totality of what points can and cannot be contained in the linear combination of classes of algebraic cycles.
The final key fact that must be mentioned is that any Swiss cheese manifold description can be associated with one unique vector formal theory in this way. That is, there is a one-to-one correspondence between Swiss cheese manifolds and a subset of the set of all vector formal theories. As we shall see, the computability of all such vector formal theories will play an important role in the proof of the negation of the Hodge Conjecture.
IV. THE PROPOSITION Q.
Now we can consider the proposition, "For all Hodge Classes of the (Swiss cheese) type described above SC, there exists a formal vector theory (as described above) with a set of axioms and a (decidable) set of inference rules such that (at least) every point that is an ordered pair of integers in the Swiss cheese manifold can be accurately depicted to be 'in the Swiss cheese manifold or out of it' based on proofs of 'second-level' V2 theorems based on the 'first-level' V1 axioms and first-level inference rules." That is: Given an S.C. Hodge Class and any vector wf in an associated particular vector formal theory, the vector wf is true if and only if there exists a point in the relevant Hodge Class that is in the "window of points" described by the wf.
It is important to note that the Hodge Conjecture implies Q. That is, if rational linear combinations of classes of algebraic cycles really can be used to express Hodge Classes, then we really can use vector formal theories, as explained above, to describe Hodge Classes.
V. PROOF THAT THE HODGE CONJECTURE IS FALSE.
Conclusion:
Assume Q. Then we have that for all Swiss-cheese-manifold Hodge Classes SC, the language consisting of 'second-level vector theory propositions based on ordered pairs of integers derived from SC that are theorems' is decidable. All subsets of the set of all ordered pairs of integers are therefore decidable, since each language based on each Hodge Class SC as described just above can be derived from its associated Swiss-Cheese Hodge Class and all subsets of all ordered pairs of integers can be associated with a Swiss-Cheese Hodge Class algebraically. In other words, elements of the set of subsets of Z x Z can be mapped to elements of the set of all Swiss-Cheese Hodge Classes with a bijection, whose elements can in turn be mapped to elements of a subset of the set of all vector formal theories with a bijection, which can in turn be mapped to a subset of the set all computable languages with a bijection, which can in turn be mapped to a subset of the set all Turing machines with a bijection. This implies that the original set, the set of all subsets of Z x Z, is countable, which is false. This establishes that the Hodge Conjecture is false, since: Hodge Conjecture —> Q —> (PowerSet(Z x Z is countable) and NOT PowerSet(Z x Z is countable)).
VI. EASILY UNDERSTOOD SUMMARY
A simple way to express the idea behind this proof is: We have articulated a logic-based way to express what might be termed “descriptions of rational linear combinations of classes of algebraic cycles.” These “descriptions” deal with “presence within a tile” in projective 2-D space of one or more points from a fixed rational linear combination of classes of algebraic cycles. This technique establishes that, when restricting attention to a particular type of Hodge Class, the Hodge Conjecture implies that there can only be countably infinitely many such “descriptions,” since each such description is associated with a computable language of “vector theorems” and thus a Turing machine. This leads to a contradiction, because there are uncountably infinitely many Swiss cheese manifolds and also uncountably infinitely many associated Hodge Classes derived from these manifolds, and yet there are only countably infinitely many of these mathematical objects if the Hodge Conjecture is true. That is why the Hodge Conjecture is false.